The invention concerns a valve combination for flame photometers comprising a switching valve and a subsequent safety valve connected thereto for either obstructing or letting pass the fuel gas emitted therefrom, wherein each valve has at least one entrance opening and one exit opening for the fuel gases.
Whenever a flame photometer is used for analysis of a test solution which is constituted by two or more elements, a double beam or multiple beam method has to be applied, in which one flame is surrounded by a plurality of optical systems including different filters, beam detectors and measuring instruments.
It is generally known that different sample elements require different maximum flame temperatures, which in turn demand different fuel gases, to provide appropriate conditions to excite the atoms of the sample elements.
Economies in test procedure, namely a least possible consumption of material and a reduction of time would result, if the fuel gas can be switched from one gas to another in a few seconds and without extinguishing the burner flame. In other words, a few seconds after the switching operation only the desired fuel gas is permitted to feed the burner of the flame photometer.
In the known flame photometer devices the switching over from one to another fuel gas lasts a few minutes including the steps of flowing supply and stoppage of the one fuel gas, and the activity of the other fuel gas.
This is due to the arrangement and the form of the gas supply valves. Such valves generally comprise a switching valve and a safety valve which only supplies the gas if at the same time the required compressed air flows out.